When I look at packages sorted by Origin in Synaptic I can see the sources I know and have added to sources.list, but there's quite a few packages under "Local" and I do not know how they got installed, and how they get upgraded. Could someone please let me know what the "repo" Local which contains 62 packages is?

Very likely, yes. Only the ones that are autoremovable (third option in the Status set - if that's what it's called in the English version) can be removed without problems. Or so they say (I've had Synaptic itself listed there once...).

Or can I remove them. I guess I can find out by trying and see what breaks

If you didn't install anything manually (you would remember, right?) then the packages are there probably because you changed repositories. Like if you were using the Debian testing repos and then changed them for the new LMDE repos (latest/incoming).If you run 'apt-get autoremove --purge' or 'deborphan' and nothing is removable then leave them there because they're needed in some way.'aptitude why package' also gives some info.

Very likely, yes. Only the ones that are autoremovable (third option in the Status set - if that's what it's called in the English version) can be removed without problems. Or so they say (I've had Synaptic itself listed there once...).

Or can I remove them. I guess I can find out by trying and see what breaks

Yeah, that'll be fun...

I spent some time on this today and got all the Local packages removed. Nothing seems to be broken and there were no complex dependency issues either. A lot of them depended on each other so it went quite smoothly. The only package I did keep was Virtualbox which I did install from a downloaded package. Now "Local" is gone and I feel much cleaner!